The Mac OS X Goes to Sea

The clarity of the chart image was outstanding.

October 4, 2007

In the article “Computer Courses” in the March 2004 issue of this magazine I commented on the lack of chart plotter programs suitable for use with the latest generation Macintosh computers, those running the excellent Unix-based OS X operating system. Fortunately my wish and that of countless other Macintosh devotees has been fulfilled with the introduction of a new chart-based navigation program, GPSNavX designed by a sailor, Rich Ray, specifically to take advantage of the outstanding stability and ease of use of OS X Panther, version 10.3.3.

Available on the web as shareware ( it took only a few seconds to download and decompress the GPSNavX program and the accompanying 836 KB summary document. I placed my PowerBook G4 on the chart table and connected the Furuno GPS-31 to the USB port via a Keyspan serial-to-USB adapter. A double click on the GPSNavX program icon had the program up and running in about six seconds. The familiar program menu bar appeared at the top of the screen. Less than eight seconds after clicking on the Auto Open command under the File menu, the chart of the local area appeared on the screen, with the boat’s position icon at the center, accompanied by two dialog boxes: one for Chart Commands, the other for the GPS Input Data.

When desired, NMEA 0183 information from a GPS (or Loran C) can be FIX and UTC information. This GPS data can also display the location presented in a dialog box to show the current LAT/LON, SOG, COG, and relative signal strength of each satellite acquired. A selectable monitor can show each successive NMEA sentence as it is received from the navigation receiver. A Settings window is used to configure the navigation data input and to distribute information to other devices, including an autopilot. Although the system can be used with an existing GPS receiver, a USB-connected, WAAS-capable GPS receiver is available for less than $120 (Rayming TN-200 USB GPS) that can make the system totally independent of the vessel’s power system by operating from the laptop’s internal battery.


Like many other Mac OS-X programs, moveable on-screen dialog boxes are used to access program control options, minimizing the need to use the pull-down menus available from the menu bar. The two most used on-screen dialog boxes, Chart Settings and GPS Management, can be made transparent to minimize obscuration of chart information or entirely hidden from view, devoting the entire 15-inch diagonal LCD screen of the G4 laptop to display of the chart.

As I experimented with the program I checked its capabilities against what I believe to be the primary functions for a successful chart plotter: a clear, precise image of the chart; ease in shifting the area of the chart in view; automatic centering of the vessel on the chart; quick change in view magnification; an ability to measure bearings and distances between any points; precise, on-screen cursor position indication; easy entry of waypoints, including their full identification; and the ability to annotate the chart with the same ease as when using paper charts, plus the option of storing the annotation with the chart data. The GPSNavX program fulfilled all of these desires. More complex chart plotter software offers additional capabilities. However, in my experience in navigation planning and in real time navigation, I have found the capabilities noted are the ones I need and use most often.


For GPSNavX Program and accessories:


For Mr. TidesX:

For BSB Charts:

For Softcharts:


For MarinePlanner, individual raster scan charts, groups of charts or chart packages:

Continuing to work by intuition, without resort to reading the “book, I explored the six Command icons and the Zoom Level window contained in the Chart Settings dialog box. The icons enable commands for: dragging the chart across the screen; designating an area to be expanded to fill the screen; measuring bearing and distance between two points (with a Great Circle used when warranted by the distance between points); creating waypoints (with a mouse click); repositioning waypoints (by dragging to a new position with the lat/lon constantly displayed adjacent to the cursor); and annotating the chart by drawing lines in any of the multitude of colors available from the OS X Panther operating system. Nine chart image zoom levels are available ranging from three percent to 200 percent. The Chart Settings dialog box can be expanded to show the Go-To waypoint, the active route and other information. The GPSNavX program will display any raster scan image or chart, like those available from BBS or Softchart. While the system does not support vector chart formats at this time, it is likely that future development will allow use of Electronic Navigational Chart (ENC) vector products from NOAA.

The clarity and readability of the chart image on the G4 PowerBook’s high resolution LCD screen was outstanding. However, as with all general-purpose LCD screen computer displays, the screen brightness is insufficient for use in any location other than a limited brightness environment such as at a sailboat’s chart table or in the wheelhouse of a motoryacht. Screen visibility in an open cockpit is zero. Full sunlight visibility can be achieved by connecting the computer’s video output to a sunlight readable screen. A radio frequency (RF) linked mouse can be used to control the remotely located (and happily protected) computer.


The program can compare the vessel’s GPS position with the charts available in the computer and automatically open the appropriate chart with the vessel positioned at the center of the screen. Waypoints, (entered with a mouse click or by lat/lon) can be designated by file number or with a description of unlimited length (if you wish you can write a book to describe a waypoint) plus any of 50 icons. The size of the waypoint identification text on the screen remains constant regardless of the chart magnification selected. Waypoints may be repositioned by dragging to a new location, with the lat/lon constantly displayed next to the cursor. Waypoints can easily be assembled into routes that can be used in forward or reverse order. The only limit on the number of waypoints, the amount of information used to identify waypoints, the number and length of routes is the storage capacity of the computer. Waypoints can be imported from or exported to other programs.

Tide information is readily available from a companion piece of Mac OS X open source software, Mr. Tides X.

In my biased opinion (I am an ardent Mac user) a Mac running OS X Panther with a USB GPS receiver and the GPSNavX program can be an unbeatable combination in those environments where the screen image is visible. Add a remote, sunlight readable, 15-inch or larger screen and an RF-coupled mouse and it will be a hard setup to beat at any location on board.


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